The number of “child” boundaries completely enclosed by this one.

A McMeasure object.  

object.mRgnNestedChildrenCount

The mRgnNestedChildrenCount Property syntax has these parts:

Each boundary can have zero or more “child” boundaries that it encloses. This measurement reports the number of those nested children.

Nesting is based on boundary polygon computations where it is assumed that boundaries are either completely enclosed or not enclosed at all. For regions that overlap without being completely nested, the nesting relationship is ambiguous: either feature may be considered the parent or they may be considered not nested at all.

Note that a “hole” and a “nested region” are different things. Holes have no effect on this measurement unless they correspond to feature boundaries (and they usually will not). See the Holes and NestedWithin properties for more discussion.